Earnings Per Share - EPS Calculation (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($) class_of_stock $ / shares shares	Jun. 30, 2021 USD ($) $ / shares shares	Jun. 30, 2022 USD ($) class_of_stock $ / shares shares	Jun. 30, 2021 USD ($) $ / shares shares
Earnings Per Share [Abstract]
Number of classes of common stock | class_of_stock	2		2
Share-based compensation awards outstanding that could be redeemed for shares of common stock (shares) | shares			0
Numerator for Basic and Diluted Earnings Per Share:
Net earnings	$ 30,765	$ 49,899	$ 66,949	$ 112,028
Undistributed earnings	30,765	49,899	66,949	112,028
Allocation of net earnings:
Undistributed earnings	30,765	49,899	66,949	112,028
Net earnings	30,765	49,899	66,949	112,028
Class A
Numerator for Basic and Diluted Earnings Per Share:
Net earnings	29,895	48,488	65,056	108,860
Dividends	0	0	0	0
Undistributed earnings	29,895	48,488	65,056	108,860
Allocation of net earnings:
Dividends	0	0	0	0
Undistributed earnings	29,895	48,488	65,056	108,860
Net earnings	$ 29,895	$ 48,488	$ 65,056	$ 108,860
Denominator:
Basic earnings per share - weighted-average shares (in shares) | shares	3,436,000	3,436,000	3,436,000	3,436,000
Effect of dilutive stock options (in shares) | shares	0	0	0	0
Diluted earnings per share - adjusted weighted-average shares for assumed conversions (in shares) | shares	3,436,000	3,436,000	3,436,000	3,436,000
Basic earnings per share (in dollars per share) | $ / shares	$ 8.70	$ 14.11	$ 18.93	$ 31.68
Diluted earnings per share (in dollars per share) | $ / shares	$ 8.70	$ 14.11	$ 18.93	$ 31.68
Class B
Numerator for Basic and Diluted Earnings Per Share:
Net earnings	$ 870	$ 1,411	$ 1,893	$ 3,168
Dividends	0	0	0	0
Undistributed earnings	870	1,411	1,893	3,168
Allocation of net earnings:
Dividends	0	0	0	0
Undistributed earnings	870	1,411	1,893	3,168
Net earnings	$ 870	$ 1,411	$ 1,893	$ 3,168
Denominator:
Basic earnings per share - weighted-average shares (in shares) | shares	200,000	200,000	200,000	200,000
Effect of dilutive stock options (in shares) | shares	0	0	0	0
Diluted earnings per share - adjusted weighted-average shares for assumed conversions (in shares) | shares	200,000	200,000	200,000	200,000
Basic earnings per share (in dollars per share) | $ / shares	$ 4.35	$ 7.06	$ 9.47	$ 15.84
Diluted earnings per share (in dollars per share) | $ / shares	$ 4.35	$ 7.06	$ 9.47	$ 15.84